Estimated reading time 12 minutes, 18 seconds.
As the Second World War came to an end in 1945, Sikorsky Aircraft began to slow its production of military helicopters. Shortly thereafter, the commercial helicopter industry came into being, with Bell Aircraft launching its Model 47, and Sikorsky debuting its S-51, to serve this fledgling market.
On the geopolitical stage, tensions between the West and Soviet Russia were simmering. The United States was very concerned that if the Soviet Union was ever to attack North America, it would be over the North Pole via Alaska and northern Canada.
Of course, the Arctic would be very dangerous for anyone stranded there during offensive or defensive operations — particularly so during the winter. Should an aircrew become stranded, immediate rescue would be paramount, and the military believed helicopters provided the most promise in terms of being able to carry out lifesaving operations. It developed plans for helicopters to be strategically placed along the northern flight corridors, despite existing rotary-wing aircraft only being able to carry three or four people.
During 1946, the Army Air Forces (which would soon become the U.S. Air Force) contacted helicopter manufacturers about a preliminary proposal specification for a polar rescue helicopter. Piasecki test pilot Leonard LaVassar recalled: “The design guidelines were daunting — capacity for 6,000 pounds [13,225 kilograms] payload; space for 30 litters; ability to carry sling-loaded trailers or building modules containing medical, communication or housing facilities; 188 miles [300 kilometers] range; and a proven advanced cruise speed.”
Pioneer Frank Piasecki developed and flew his prototype twin-rotor 12-place HRP-1 Rescuer helicopter during 1947. The predecessor to the HRP-1 was Piasecki’s twin-rotor XHRP-X “Dogship,” which first flew in March 1945. It was the largest helicopter at the time, but it was obvious that in the future, even larger transport helicopters would be required for any proposed search-and-rescue (SAR) duties in the far north.
In 1948, the Piasecki Helicopter Company was declared the winner of the U.S. Air Force (USAF) competition. Within two years, Piasecki had completed preliminary design, wind tunnel testing, and full-scale mockup construction of its proposed aircraft, which was called the Piasecki Model PV-15/XH-16.
The USAF was still not sure that the helicopter industry would be able to construct a helicopter many times larger than those presently flying, and wanted to test the concept prior to going into full production.
However, in 1950, Piasecki received a follow-up contract from the USAF for two prototypes, along with data and publications, all flight-testing, spare parts and any needed special tools. Such an award was unprecedented for a small company, and the resulting aircraft would represent a leap in helicopter technology for Frank Piasecki. It would also be by far the largest helicopter in the world.
Interest from across the services
The massive XH-16 went from blueprint to a completed rescue and transport rotary-wing aircraft by early 1953. The silver metal fuselage measured 78 feet (23.8 meters) from the nose to the tail, 9.6 feet (2.9 meters) across, with an estimated 2,500-cubic-foot (70.8-cubic-meter) capacity. It had two three-bladed metal main rotor blades, each with a diameter of 82 feet (25 meters). The H-16’s landing gear had two main wheels forward and a tail wheel aft near the entrance ramp.
Power for the helicopter came from two Pratt and Whitney piston R-2180-11 radial engines, each producing 1,650 horsepower.
It was not long before the U.S. Army also became very interested in the project, and it actively offered support for the new XH-16. The aircraft even impressed Piasecki’s own shop floor workers; the enormous machine was a sight to see.
The first flight of the YH-16 (now service-test) Transporter helicopter took place on Oct. 23, 1953, at the Philadelphia, Pennsylvania, airport. Test pilots Harold Peterson and Phil Camerano were in the cockpit for the initial 12-minute flight.
The empty weight of the XH-16 was 32,000 lb. (14,500 kg), with a useful load of 14,000 lb. (6,350 kg). Its maximum speed was 123 mph (198 km/h), with a cruise speed of 110 mph (177 km/h). It had a range of 230 miles (370 kilometers), and a ceiling with a normal load of 18,000 feet (5,490 meters).
The helicopter carried 40 passengers or 32 litters, plus an aircrew of three. If not carrying passengers, it could transport up to three Jeeps or small vehicles.
Tests continued with the YH-16, but it became apparent that the piston-powered helicopter was going to need turbine engines in order to meet USAF requirements in the remote Arctic for rescue operations and future missions.
Piasecki engineers were soon designing an upgraded H-16 transport helicopter (known as the YH-16A). This was based on the earlier flying prototype, but included YT38-A-10 turbine engines designed and manufactured by General Motors Allison Division. They were considerably smaller and lighter than piston engines of comparable power. The extra space they freed up in the YH-16A’s interior could be used for more passengers and cargo.
The aircraft was ready for its first flight in July 1955, just two years after the YH-16 had first flown. Piasecki issued a press release on Dec. 6, 1955, announcing the first public flight demonstration of the world’s largest turbine transport helicopter at the Philadelphia International Airport.
The upgraded YH-16A was faster and could carry greater loads than its predecessor. The press release also claimed the aircraft was easy to fly and maintain, needed no warm-up, and provided greater comfort for passengers and crew due to the use of gas turbine powerplants.
The helicopter demonstrated its ability to fly and maintain altitude with a normal load with one of its engines shut off during flight tests. This demonstration of multi-engine reliability, in addition to autorotative flight with both engines off, was another advancement in air transportation safety.
The empty weight of the YH-16A was 22,500 lb. (10,200 kg), with a useful load of 11,070 lb. (5,020 kg). Its maximum speed was 146 mph (235 km/h), with a cruise speed of 140 mph (225 km/h). Its range was 230 miles (370 kilometers), with a ceiling with a normal load of 19,100 feet (5,820 meters).
Bigger, faster, stronger
In December 1955, the Piasecki turbine YH-16A reached an unprecedented speed of 166 mph (265 km/h) during calibration flight test runs. This was 10 mph (16 km/h) faster than the official helicopter speed record set by the Sikorsky XH-39 turbine helicopter. Test pilot Peterson said the YH-16A “handles easier, with flying qualities more similar to those of fixed-wing aircraft, than smaller helicopters.”
Chief pilot LaVassar, although not the main pilot on the YH-16A, logged some time flying the helicopter. “The Transporter’s fuselage was rock solid during turn-ups, and the absence of any pitching, rolling or vibration was a pleasant surprise for the project pilots,” he later wrote in an article about the aircraft. “The rotors seem to swing lazily through the air at the normal operating speed of just 147 rpm, almost slow enough for observers to count the blades as they turned.”
LaVassar found that both prototypes were responsive to light control pressures, contemptuous of rough air, and delightful to control throughout their flight envelopes.
The Transporter surprised everyone with its absence of shaking, to the extent that there was no need for vibration reduction devices. LaVassar found the helicopter a joy to fly. Test flights demonstrated the exceptional capabilities of the H-16 design in performance, handling qualities, speed, external payload, structural integrity, and operational suitability.
As test flights continued on the YH-16A, Piasecki’s engineers were envisioning an even larger third transport helicopter capable of carrying a greater payload with higher speeds. It was designed to carry up to 69 troops. This new helicopter, called the Piasecki PH-45 and PH-45A/YH-16B was planned to be the production version of the “Turbo Transporter.”
Even more powerful Allison turbine engines were planned for the production version of the YH-16B. Piasecki engineers even proposed two landing gear versions of the YH-16B — a short gear and a tall gear version. The idea was that an interchangeable pod could be attached under the fuselage of the tall-gear version. The tall-gear version planned to have a gross weight of 44,500 lb. (20,185 kg), and it would be capable of transporting a 13,000 lb.- (5,902 kg)-payload 175 nautical miles (280 kilometers).
Unfortunately, the upgraded versions of the tandem-rotor transport YH-16B never saw the light of day. On Jan. 5, 1956, during its final test phase, the YH-16A crashed near the Delaware River while returning from a flight over New Jersey. The two test pilots on board — Harold Peterson and George Callahan — were fatally injured.
The resulting accident investigation indicated that the rear rotor shaft had failed. The aft rotor blades desynchronized, allowing them to contact the forward rotors. The cause was determined to be a frozen bearing in the test instrumentation, which allowed an undetectable groove to form within the shaft.
“The investigation determined no design flaw, structural failure, engine or dynamic system problem contributed to the Transporter’s loss,” said LaVassar. “Instead, a mechanical component of temporarily-installed instrumentation gave way, bringing the aircraft down.”
With the loss of the YH-16A, the USAF sadly decided to cancel and abandon the Transporter helicopter program.